Combined biological and cement solidification of lead-zinc tailings for backfill preparation and its environmental effects

Lead-zinc tailings (LZT) are known to contain excess lead (Pb) and zinc (Zn), posing potential environmental and human health risks if not properly managed. Cemented paste backfill (CPB) technology is a commonly used method for reutilizing waste tailings. However, the release of heavy metals from LZT after backfilling can be exacerbated by in-situ stress and surrounding pH conditions, leading to secondary environmental pollution and undermining mine stability. To address this problem, a novel and efficient in-situ encapsulated approach was proposed in this study. A biocemented lead-zinc tailing backfill (BPTB) was prepared by mixing cement, microbial solution, lead-zinc tailings, and water, with the aim of reducing the leaching behavior of lead-zinc and achieving environmentally friendly backfilling. To validate the feasibility of this approach, a comprehensive series of physical, chemical, and characterization tests were conducted to evaluate the mechanical properties and environmental impact of BPTB. The results revealed that both cement and microbial solutions effectively immobilized lead-zinc, with the synergy of biomineralization and hydration maintaining the pH around 8 as well as minimizing the release of Pb and Zn. The leaching behavior of lead-zinc in samples treated with biosolution additives decreased by 43% and 75%, respectively, falling below the regulatory limits. Furthermore, biomineralization reduced the inhibitory effect of lead-zinc on cement hydration, resulting in a remarkable increase in the strength of BPTB by 115.2%−159.5% compared to conventional CPB. Additionally, the diffusion rate of Zn was found to be faster than that of Pb in the multi-competitive system. The test results validated the environmentally friendly backfilling potential of BPTB, thereby promoting the recycling and sustainable development of lead-zinc tailings.